1. Field of the Invention
The present invention relates to a projection lens and a projection display apparatus, and more specifically to a projection lens preferably used for magnifying and projecting an original image formed, for example, by a light valve onto a, screen, and a projection display apparatus using the same.
2. Description of the Related Art
Recently, projection projectors (projection display apparatuses) that use a DMD (Digital Micro-mirror Device: registered trade mark) display device as the light valve have been used instead of liquid crystal display apparatuses. Unlike liquid crystal display apparatuses, DMD display apparatuses have less amount of light loss as they do not need to polarize the projected light and are superior in accuracy of gray-scale representation over crystal display apparatuses. In a projection display apparatus, the DMD controls the reflection directions of light from the light source according to inputted video signals using high reflectance small rectangular mirrors capable of changing the inclination within a range of about 10 degrees or more to focus only the desired reflection light beams on a screen, thereby enabling projection of the image. This is achieved by arranging, for example, several millions of mirrors on a substrate and digitally controlling all of the mirrors independently, in which each mirror corresponds to each pixel of the projected image.
As for the projection lenses applicable to projection display apparatuses that use a DMD as the light valve, those described in Japanese Unexamined Patent Publication No. 2012-220875 and Japanese Patent No. 4683944 are proposed. Japanese Unexamined Patent Publication No. 2012-220875 describes a projection lens formed of 10 or 11 lenses in which aspherical plastic lenses are used for the most magnification side lens and the third lens from the magnification side. Japanese Patent No. 4683944 describes a projection lens formed of 14 lenses in which an aspherical plastic lens is disposed on the most magnification side.